To me the most annoying characters, if specifically looking at protagonists, are ones who are simply dragged along for the story and only progress the plot at the behest of others. They never make their own decisions.
As for other types of characters, the most annoying ones are the ones that butt in, add nothing to the story, and they get too much screentime. And often they're just there for 'comedic relief'.
As for what's spicy, the characters have to have a need for each other. And the sex can't be too frequent; give the reader time to breathe and let the characters do other things! Even if it's full on erotica, scenes need to be built up before sexy times begin. Otherwise it can become monotonous and not have as big of an impact, like at that point you're just reading porn clips one after the other without much context.